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The current code is incredibly resilient to updates to the spec and has worked quite well so far. However, recent implementations expose a weakness in that this is rather slow. A large part of it is written in assembly, making it opaque to the compiler for optimisations. The future proofness requires reading registers that are effectively `volatile`, making it even harder for the compiler, as well as adding lots of implicit barriers, making it hard for the microarchitecutre to optimise as well. We can make a few assumptions, checked by a few well placed asserts, and remove a lot of this burden. For a start, at the moment there are 4 group 0 counters with static assignments. Contexting them is a trivial affair that doesn't need a loop. Similarly, there can only be up to 16 group 1 counters. Contexting them is a bit harder, but we can do with a single branch with a falling through switch. If/when both of these change, we have a pair of asserts and the feature detection mechanism to guard us against pretending that we support something we don't. We can drop contexting of the offset registers. They are fully accessible by EL2 and as such are its responsibility to preserve on powerdown. Another small thing we can do, is pass the core_pos into the hook. The caller already knows which core we're running on, we don't need to call this non-trivial function again. Finally, knowing this, we don't really need the auxiliary AMUs to be described by the device tree. Linux doesn't care at the moment, and any information we need for EL3 can be neatly placed in a simple array. All of this, combined with lifting the actual saving out of assembly, reduces the instructions to save the context from 180 to 40, including a lot fewer branches. The code is also much shorter and easier to read. Also propagate to aarch32 so that the two don't diverge too much. Change-Id: Ib62e6e9ba5be7fb9fb8965c8eee148d5598a5361 Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com> |
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Trusted Firmware-A ================== Trusted Firmware-A (TF-A) is a reference implementation of secure world software for `Arm A-Profile architectures`_ (Armv8-A and Armv7-A), including an Exception Level 3 (EL3) `Secure Monitor`_. It provides a suitable starting point for productization of secure world boot and runtime firmware, in either the AArch32 or AArch64 execution states. TF-A implements Arm interface standards, including: - `Power State Coordination Interface (PSCI)`_ - `Trusted Board Boot Requirements CLIENT (TBBR-CLIENT)`_ - `SMC Calling Convention`_ - `System Control and Management Interface (SCMI)`_ - `Software Delegated Exception Interface (SDEI)`_ The code is designed to be portable and reusable across hardware platforms and software models that are based on the Armv8-A and Armv7-A architectures. In collaboration with interested parties, we will continue to enhance TF-A with reference implementations of Arm standards to benefit developers working with Armv7-A and Armv8-A TrustZone technology. Users are encouraged to do their own security validation, including penetration testing, on any secure world code derived from TF-A. More Info and Documentation --------------------------- To find out more about Trusted Firmware-A, please `view the full documentation`_ that is available through `trustedfirmware.org`_. -------------- *Copyright (c) 2013-2019, Arm Limited and Contributors. All rights reserved.* .. _Armv7-A and Armv8-A: https://developer.arm.com/products/architecture/a-profile .. _Secure Monitor: http://www.arm.com/products/processors/technologies/trustzone/tee-smc.php .. _Power State Coordination Interface (PSCI): PSCI_ .. _PSCI: http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf .. _Trusted Board Boot Requirements CLIENT (TBBR-CLIENT): https://developer.arm.com/docs/den0006/latest .. _SMC Calling Convention: http://infocenter.arm.com/help/topic/com.arm.doc.den0028b/ARM_DEN0028B_SMC_Calling_Convention.pdf .. _System Control and Management Interface (SCMI): SCMI_ .. _SCMI: http://infocenter.arm.com/help/topic/com.arm.doc.den0056a/DEN0056A_System_Control_and_Management_Interface.pdf .. _Software Delegated Exception Interface (SDEI): SDEI_ .. _SDEI: http://infocenter.arm.com/help/topic/com.arm.doc.den0054a/ARM_DEN0054A_Software_Delegated_Exception_Interface.pdf .. _Arm A-Profile architectures: https://developer.arm.com/architectures/cpu-architecture/a-profile .. _view the full documentation: https://www.trustedfirmware.org/docs/tf-a .. _trustedfirmware.org: http://www.trustedfirmware.org